Saturn’s ‘Death Star’ moon may not conceal an ocean after all

Craters blemish Saturn’s moon Mimas, including a large one that makes the moon look like the Death Star in Star Wars. A lack of cracks on the moon’s surface, though, casts doubt on the presence of a subsurface ocean, new research suggests.
JPL-CALTECH/NASA, SPACE SCIENCE INSTITUTE

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Saturn’s ‘Death Star’ moon may not conceal an ocean after all

By Thomas Sumner

An ocean of liquid water probably doesn’t lurk beneath the icy surface of Mimas, Saturn’s smallest major moon, new calculations suggest. Scientists had proposed the ocean in 2014 to help explain an odd wobble in the moon’s orbit.

Other ocean-harboring moons, such as Jupiter’s Europa and Saturn’s Enceladus, are crisscrossed by fractures opened by strong tides that cause their oceans to bulge outward. Mimas, though freckled with craters, lacks any such cracks.

Planetary scientist Alyssa Rhoden of Arizona State University in Tempe and colleagues calculated whether Mimas’ icy shell could withstand the stress of a subsurface ocean pushing outward. Taking into account the moon’s elongated orbit, the researchers estimate that a subsurface ocean would produce tidal stresses larger than those on crack-riddled Europa. Mimas therefore probably doesn’t have an ocean, the researchers conclude February 24 in the Journal of Geophysical Research: Planets.